Fingerprint input apparatus

ABSTRACT

A fingerprint input apparatus includes scattered light and a two-dimensional image sensor. The scattered light is generated inside a finger having a fingerprint pattern in accordance with external light. The fingerprint pattern is made up of a ridge portion and a valley portion. The two-dimensional image sensor is made of a large number of light-receiving elements arranged in a two-dimensional array. The image of the fingerprint pattern is input to a light-receiving surface of the light-receiving element. The light-receiving element whose light-receiving surface is in substantially contact with the ridge portion detects as the ridge portion a bright portion where the scattered light emerging from the finger reaches at a high intensity. The light-receiving element whose light-receiving surface corresponds to the valley portion via a space detects as the valley portion a dark portion where the scattering light emerging from the finger reaches at a low intensity.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 09/494,506filed Jan. 31, 2000 now U.S. Pat. No. 6,829,375, the benefit of thefiling date of which is hereby claimed.

BACKGROUND OF THE INVENTION

The present invention relates to a fingerprint input apparatus and, moreparticularly, to a fingerprint input apparatus capable of directlyreading a fingerprint image using a two-dimensional image sensor.

In a conventional fingerprint input apparatus of this type, the skinsurface of the fingertip is irradiated with light at a predeterminedangle using optical components such as a lens and prism or a fiber. Thelight reflected by the skin surface is focused to output a fingerprintimage. Alternatively, a study has been made on a scheme of directlyinputting a fingerprint image using an electrostatic capacitance insteadof obtaining a fingerprint image using the optical system.

In these conventional fingerprint input apparatuses, when the opticalcomponents such as a lens and prism or a fiber are used, a space for thesizes of these optical components and their mounting positions isrequired to result in a large thickness and size of the apparatus. Inaddition, since these optical components are relatively expensive, theapparatus cannot be manufactured at low cost. When the fingerprint imageis optically processed using these optical components, the resultantimage tends to distort.

The scheme of directly inputting a fingerprint image using theelectrostatic capacitance is susceptible to external static electricityand difficult to obtain a high sensitivity.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a relativelylow-profile, compact, inexpensive fingerprint image input apparatus.

It is another object of the present invention to provide a fingerprintimage input apparatus capable of obtaining an image free fromdistortion.

In order to achieve the above objects of the present invention, there isprovided a fingerprint input apparatus comprising scattered lightgenerated inside a finger having a fingerprint pattern in accordancewith external light, the fingerprint pattern being made up of a ridgeportion and a valley portion, and a two-dimensional image sensor made ofa large number of light-receiving elements arranged in a two-dimensionalarray, an image of the fingerprint pattern being input to alight-receiving surface of the light-receiving element, wherein thelight-receiving element whose light-receiving surface is insubstantially contact with the ridge portion detects as the ridgeportion a bright portion where the scattered light emerging from thefinger reaches at a high intensity, and the light-receiving elementwhose light-receiving surface corresponds to the valley portion via aspace detects as the valley portion a dark portion where the scatteringlight emerging from the finger reaches at a low intensity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the schematic arrangement of a fingerprintinput apparatus according to the first embodiment of the presentinvention;

FIG. 2 is a view showing the light-receiving state of a two-dimensionalimage sensor shown in FIG. 1;

FIG. 3 is a view showing the schematic arrangement of a fingerprintinput apparatus according to the second embodiment of the presentinvention;

FIG. 4 is a view showing the schematic arrangement of a fingerprintinput apparatus according to the third embodiment of the presentinvention; and

FIG. 5 is a view showing the schematic arrangement of a fingerprintinput apparatus according to the fourth embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail with reference to theaccompanying drawings.

FIG. 1 shows a fingerprint input apparatus according to the firstembodiment of the present invention. Referring to FIG. 1, referencenumeral 11 denotes a two-dimensional image sensor (to be referred to asan image sensor hereinafter) for two-dimensionally detecting the lightintensity in accordance with the three-dimensional pattern of a skinsurface 3 of a finger 2; 12, an image processor for image-processing anoutput from the image sensor 11 to generate a fingerprint pattern; and13, a pattern recognition unit for extracting the features of thefingerprint pattern generated by the image processor 12 and recognizingthe pattern by comparing the extracted features with a predeterminedreference pattern.

The image sensor 11 comprises a substrate 16 and a large number oflight-receiving elements 1 two-dimensionally arranged in a matrix on thesubstrate 16. A two-dimensional image is formed on the basis of anoutput from each light-receiving element 1. As shown in FIG. 2, atransparent cover 1B comprising a transparent member made of glass isformed on the image sensor 11 to protect a light-receiving surface 1A ofeach light-receiving element 1.

The pitch of the light-receiving elements 1 must be smaller than thepitch of ridge portions (projections) 4 or valley portions (recesses) 5of the skin surface 3. If the pitch of the light-receiving elements 1 is50 μm or less, an image having precision enough to perform patternrecognition can be obtained. A CCD (Charge-Coupled Device) sensor isused as the image sensor 11.

In this embodiment, scattered light emerging from the finger 2 isgenerated by ambient light of the finger 2 without using any lightsource. The image processor 12 and pattern recognition unit 13 constructa fingerprint recognition section 10 and can be made up of knowncircuits.

To recognize the skin surface 3 of the finger 2, as shown in FIG. 2, thefinger 2 is placed on the image sensor 11 such that the skin surface 3is in contact with the transparent cover 1B. At this time, the ridgeportions 4 of the skin surface 3 are in contact with the transparentcover 1B of the image sensor 11. Scattered light from the inside of thefinger 2 is directly received from the ridge portions 4 to thelight-receiving elements 1 via the transparent cover 1B.

A space 6 is formed between the transparent cover 1B and each valleyportion 5 of the skin surface 3. Scattered light emerging from thefinger 2 to the space 6 via the valley portion 5 is refracted andscattered at the interface between the skin and air and is then diffusedin the space 6. The amount of light reaching the light-receiving elementvia the space 6 greatly reduces.

Part of light reaching the transparent cover 1B is reflected on thesurface of the transparent cover 1B due to the relationship between theincident angle on the transparent cover 1B and the refractive indices ofthe air and transparent cover 1B in the space 6. While light from theridge portion 4 directly contacting the transparent cover is detected ata high intensity, while light reaching from the valley portion 5 via thespace 6 is detected at a low intensity. Therefore, the ridge portion 4is detected as a bright portion, while the valley portion 5 is detectedas a dark portion.

As described above, the light-receiving elements 1 whose light-receivingsurfaces 1A are almost in contact with the ridge portions 4 detect asthe ridge portion 4 the bright portion that the scattered light from theinside of the finger 2 reaches at a high intensity. The light-receivingelements 1 whose light-receiving surfaces 1A correspond to the valleyportion 5 and the space 6 detect as the valley portion 5 the darkportion where scattered light from the inside of the finger 2 reach at alow intensity.

According to this embodiment, the optical components such as a lens andprism or a fiber are not required. As compared with a conventionalstructure, limitations on the physical sizes by the sizes of opticalcomponents themselves and their mounting positions can be eliminated.For example, a low-profile, compact fingerprint input apparatus having asize enough to be incorporated in an IC card required for verificationof a cardholder can be implemented. Since optical processing by opticalcomponents need not be performed, special image correction processingneed not be performed to obtain a fingerprint image free fromdistortion, thereby increasing the recognition ratio of the fingerprintpattern.

FIG. 3 shows the schematic arrangement of a fingerprint input apparatusaccording to the second embodiment of the present invention.

In the first embodiment, the scattered light from the inside of thefinger 2 is generated by the ambient light of the finger 2. For thisreason, any special light source need not be provided. However, when afingerprint input apparatus is used in a place where no ambient light isavailable, a light source such as an LED (Light-Emitting Diode) isarranged to irradiate the finger 2.

Referring to FIG. 3, reference numeral 14A denotes a light sourcearranged on the same surface side as that of an image sensor 11 so as tooppose a finger pad portion 2A of a finger 2. The finger pad portion 2Ais irradiated upward with light from the light source 14A to generatescattered light inside the finger 2. As compared with the case in whichthe light source is disposed above the finger 2 to irradiate it, thelight source does not interfere with operation of placing the finger 2on the image sensor 11, thereby implementing an easy-to-handle apparatusfor a user.

Since the distance between the light source 14A and the finger 2 is verysmall, light from the light source 14A can be guided to the inside ofthe finger 2 to allow effectively generating scattered light. Since thelight from the light source 14A does not directly reach alight-receiving element 1, the contrast is suppressed to reduce noise.

The fingertip of the finger 2 may be obliquely irradiated with lightfrom the light source 14A. In this case, scattered light can beefficiently generated inside the finger 2.

FIG. 4 shows the schematic arrangement of a fingerprint input apparatusaccording to the third embodiment of the present invention.

Referring to FIG. 4, reference numeral 14B denotes a light sourcearranged on the same surface side as that of an image sensor 11 so as tooppose a fingertip portion 2B of a finger 2. The fingertip portion 2B isirradiated obliquely upward with light from the light source 14B togenerate scattered light inside the finger 2.

According to this embodiment, since the fingertip portion 2B has analmost hemispherical surface curved downward in the forward direction,scattered light can be uniformly generated inside the finger 2 uponirradiating the finger 2 with the light from the light source 14B.

FIG. 5 shows the schematic arrangement of a fingerprint input apparatusaccording to the fourth embodiment of the present invention.

Referring to FIG. 5, a pair of light sources 14A and 14B as in thoseshown in FIGS. 3 and 4 can be arranged to interpose an image sensor 11between them.

Light sources for emitting near-infrared rays, e.g., near-infrared LEDscan be used as the light sources 14A and 14B, and a thin film filter 15for transmitting near-infrared rays and reducing disturbance light suchas visible light can be arranged, as shown in FIG. 3. In this case, animage sensor capable of receiving a near-infrared ray must be selectedas the image sensor 11. A general CCD image sensor can receive thenear-infrared rays.

According to this modification, since disturbance light such as lightfrom a fluorescent lamp or sunbeam can be reduced, noise caused by thedisturbance light can be reduced to allow efficiently inputting afingerprint image even in an environment where a large number ofdisturbance light components are present. A transparent cover 1B may becomprised of a cover having the function of a filter 15. In this case,the number of components can be reduced.

As has been described above, according to the present invention, opticalcomponents such as a lens and prism or a fiber can be omitted. For thisreason, as compared with a conventional structure, limitations on thephysical sizes by the sizes of optical components themselves and theirmounting positions can be eliminated. A low-profile, compact apparatuscan be implemented.

Since optical processing by the optical components need not beperformed, a fingerprint image free from distortion can be obtainedwithout performing special image correction processing. The recognitionratio of the fingerprint pattern can increase.

1. An imaging sensor adapted to generate an electrical signal representing and image of a skin surface of a finger, said image sensor comprising: a transparent cover having first and second surfaces; and a plurality of light responsive elements arranged under said second surface of said cover, when said first surface of said cover is in contact with said skin surface of said finger, said light responsive elements being responsive only to light directly emerging from an inside of said finger through said cover to generate said electrical signal representing said image of said skin surface of a finger.
 2. An image sensor adapted to generate an electrical signal representing an image of a skin surface of a finger, said image sensor comprising a plurality of light responsive elements, at least one of which is disposed between a ridge and a valley of a fingerprint, light from outside said finger entering said finger and emerging from said finger as scattered light, said plurality of light responsive elements generating said electrical signal representing an image of a skin surface of a finger only from scattered light directly emerging from an inside of said finger and not reflected light from outside of said finger.
 3. An image sensor adapted to generate an electrical signal representing an image of a skin surface of a finger, said image sensor comprising: a transparent cover having first and second surfaces; and a plurality of light responsive elements arranged under said second surface of said cover, when said first surface of said cover is in contact with said skin surface of said finger, said plurality of light responsive elements generating said electrical signal representing an image of a skin surface of a finger from scattered light directly emerging from an inside of said finger without a light source under said transparent cover.
 4. An image sensor adapted to generate an electrical signal representing an image of a skin surface of a finger, said image sensor comprising: a transparent cover having first and second surfaces; and a plurality of light responsive elements arranged under said second surface of said cover, when said first surface of said cover is in contact with said skin surface of said finger, said plurality of light responsive elements generating said electrical signal representing an image of a skin surface of a finger from scattered light directly emerging from an inside of said finger without a light source irradiating said skin surface in contact with said cover.
 5. An imaging sensor adapted to generate an electrical signal representing and image of a skin surface of a finger, said image sensor comprising: a transparent cover having first and second surfaces; and a plurality of light responsive elements arranged under said second surface of said cover, when said first surface of said cover is in contact with said skin surface of said finger, said light responsive elements being responsive to light directly emerging from an inside of said finger through said cover to generate said electrical signal representing said image of said skin surface of a finger, wherein no optical component is interposed between said transparent cover and said plurality of light responsive elements.
 6. An image sensor adapted to generate an electrical signal representing an image of a skin surface of a finger, said image sensor comprising: a transparent cover having first and second surfaces; and a plurality of light responsive elements arranged under said second surface of said cover, when said first surface of said cover is in contact with said skin surface of said finger, said plurality of light responsive elements generating said electrical signal representing an image of a skin surface of a finger from scattered light directly emerging from an inside of said finger, wherein no optical component is interposed between said transparent cover and said plurality of light responsive elements.
 7. A fingerprint input apparatus for inputting a fingerprint of a tip of a finger having ridge and valley portions, said fingerprint input apparatus comprising: a number of light receiving elements arranged in a two-dimensional matrix; and a transparent cover that protects a light receiving surface of said light receiving elements, wherein when a finger is placed on said transparent cover, and wherein no dedicated light source is required, a bright area is detected as a ridge portion, said bright area is such an area which a diffusion light sufficiently reaches from an inside of a finger via said ridge portion, said bright area is detected by a light receiving element having a light receiving surface close to said ridge portion, and a dark area is detected as a valley portion, said dark area is such an area which a diffusion light hardly reaches from an inside of a finger, and said dark area is detected by a light receiving element having a light receiving surface close to said valley portion. 